An electric field measurement device detects an electric field and generates electrical signals representing intensity of the electric field. The electric field measurement device may be used for various applications. For example, an electric field measurement device may be utilized as a human body communication device which performs data communication between wearable computers. An electric field measurement device may be utilized as a basic element of an electroencephalograph, which measures brain activity of a subject such as a human or animal, or another measurement device, which detects biological processes. The electric field measurement device utilized as an electroencephalograph may be situated outside the body of a subject to detect a resultant variation in an electric field from brain activity. It may be important qualities for these applications that the electric field measurement device has high sensitivity, a small size and high resistance to impact.
An electric field measurement device may include an electro-optic crystal. The electric field measurement device applies an electric field to the electro-optic crystal to induce an electro-optic (EO) effect. The electric field measurement device may use the electro-optic effect to detect an electric field in a non-contact manner.
As a result of the electro-optic effect, there is a change in optical characteristics of the electro-optic crystal such as a refractive index. A user using the electric field measurement device changes the refractive index of the electro-optic crystal and causes light to enter the electro-optic crystal. A phase of the light is changed in the electro-optic crystal. A change in intensity or phase of emission light emitted from the electro-optic crystal is electrically detected.
The electric field measurement device utilizing the electro-optic effect optically transmits detection signals representing a detected electric field. Therefore, the detection signals are less susceptible to induction or electrical noise. Since the electro-optic effect of the electro-optic crystal is utilized, the electric field measurement device may be responsive. In addition, the electric field measurement device may transmit the detection signals with little loss.
A resultant change in refractive index from the electro-optic effect is slight. Therefore, some of conventional electric field measurement devices, which use the electro-optic effect, utilize a phase change in light entering a non-linear optical crystal with the electro-optic effect. Other conventional electric field measurement devices may utilize an interferometer to improve sensitivity (c.f. Patent Documents 1 to 3).
Conventional electric field measurement devices are likely to be susceptible to environmental changes. Or, it is required that complex structures are incorporated into a conventional electric field measurement device in order to make the conventional electric field measurement device less susceptible to environmental changes.
Patent Document 1: JP 2003-98205 A
Patent Document 2: JP H07-151804 A
Patent Document 3: JP H11-194146 A